DESCRIPTION: The leukocyte NADPH oxidase is the enzyme responsible for superoxide production by phagocytes and B lymphocytes. It is dormant in resting cells but comes to life when the cells are activated. Studies of oxidase activation in cell-free systems have used anionic detergents as activating agents, but oxidase activation in whole cells is accomplished by phosphorylation. As an extension of a study from another group, a kinase dependent cell-free activating system has been developed that will be used to study oxidase activation by what is probably the physiological route. Therefore, one aim of the present work is to characterize the kinase-dependent cell-free activating system, particularly with respect to effects on the membrane. The other aim concerns the further characterization of p67phox, an NADPH-binding oxidase component. The inactivation of p67phox by NADPH dialdehyde, an affinity label, will be studied in detail. In addition, p67phox will be purified in quantity, crystallized in the absence and presence of NADPH and analyzed by X-ray crystallography.